Superheterodyne circuit arrangement



June 2, 1936.

O. SCHRIEVER SUPERHETERODYNE CIRCUIT ARRANGEMENT Filed April 20, 1933 1'7 ilula i151 INVENTOR 0770 SUM/5V5? ATTORNEY Patented June 2, 1936 UNITED STATES PATENT OFFICE SUPERHETERODYNE CIRCUIT ARRANGEIVIENT tion of Germany Application April 20, 1933, Serial No. 666,994 In Germany April 27, 1932 2 Claims.

ing of the grid or receiver circuit and on the other hand to prevent radiation of the heterodyne frequency by the antenna. For medium wave length such circuits operate in a satisfactory manner. In working at shorter wave lengths,

however, such as the so-called ultra short wave lengths, the neutralization and operation of such circuits becomes more and more difficult.

It is accordingly an object of this invention to obviate these difficulties by providing a vacuum tube detector, amplifier and oscillator having a plurality of grids and so arranging the circuits that the local oscillation frequency is applied to one grid and the incoming signal frequency to a difierent grid.

A further object of the invention is to prevent the local oscillation frequency from having any appreciable effect on the tuning of the control grid circuit to the signal frequency by means of a screen grid.

A still further object of the invention is to provide a space charge grid which may be used in a superheterodyne detector in connection with the other grids mentioned.

Other objects of the invention will become apparent to those skilled in the art as the description thereof proceeds. A preferred form of the invention is shown in the accompanying drawing in which, the single figure shows schematically the arrangement of. the circuits and also of the grid elements within the tube.

As shown the vacuum tube oscillator and detector ID has a cathode 4 and an anode or plate 9 and in the electron stream between these elements are placed at least three control elements or grids 6, I and 8 each located so that it will serve to control the electron stream in accordance with the potential applied to it. The control grid 6 may be connected to a resonant circuit 2, 3 tunable to the incoming signal frequency by a variable condenser 3. As shown coil 2 may be inductively coupled to a coil I in an antenna circuit. In the plate circuit a coil I4 and condenser I5 form a resonant circuit tunable to the heterodyne or local oscillation frequency by adjustment of a variable condenser I 5.

The intermediate or beat frequency may be derived across the terminals II and I2 of an impedance in the plate circuit, which impedance may be of any preferred form and is diagrammatically represented by element I3.

As shown, the tube is caused to oscillate by coil I4 being magnetically coupled to a coil I6 in circuit with the grid 8 located near the anode 9. While the feedbackis here shown as inductive it will be understood that any other known type of feedback coupling may be used instead. Interposed between grids 6 and 8 is a grid 1 which serves as a screen grid and effectively prevents the oscillator circuit or potentials on grid 8 from reacting on the input or circuit of control grid 6. A condenser I! connected to the screen grid and to one leg of filament 4 serves to dissipate any radio frequency potential accumulating on grid I and to maintain it at ground potential with respect to radio frequency. In some instances I also find it advisable to utilize a space charge grid 5 located between cathode 4 and control grid 6. Suitable potentials may be supplied to the plate and several grids by any voltage source, such as battery B.

The advantage of the circuit above described over known arrangements resides in the simplicity, safe operation and the omission of any neutralization adjustment when tuning. For the first time by means of this circuit has the construction of ultra short wave television receivers which can be properly operated by the layman, become such that it may be carried out economically.

Having described my invention what I claim is:

1. A vacuum tube demodulator for a superheterodyne receiver, comprising a cathode and plate, two control grids located therebetween, means for applying a signal frequency to one of said control grids, a feedback connection between the plate circuit and said second control grid, a coil and condenser connected in series in the plate circuit and forming a circuit resonant to the heterodyne frequency, and means for preventing interaction between said control grids comprising a screen grid interposed between said control grids and a. by-pass condenser connected between said screen grid and the cathode.

2. A combined vacuum tube oscillator and detector comprising a cathode, a plate, a signal control grid, an oscillator grid located between said signal grid and said plate, a circuit connecting said cathode and plate including the series connection of a source of positive potential, a circuit resonant to the heterodyne frequency and a reacta'nce having high impedance to the intermediate frequency produced, a circuit connecting said cathode and oscillator grid and including a feedback connection to the circuit resonant to the heterodyne frequency, a screen grid located between said signal control grid and said oscillator grid, a by-pass condenser connected for impressing a positive potential on said screeii grid 1ess than that applied to said plate, and a connection between said signal control grid and said cathode including a circuit which is adjustably resonant to the incoming signal frequency. V

OTTO SCHRIEVER.

between the screen grid and the cathode, means... 

